1. Field of the Invention
This invention relates to a semiconductor light emitting device and its manufacturing method especially suitable for application to semiconductor lasers and light emitting diodes using nitride-family III-V compound semiconductors.
2. Description of the Related Art
In recent years, semiconductor lasers using nitride-family III-V compound semiconductors such as AlGaInN and others have been a subject of vigorous researches and developments as semiconductor lasers capable of emitting light from the blue region to the ultraviolet region required for enhancing the density of optical discs, and some have already been brought into practical use.
Semiconductor lasers having been reported heretofore include an electron-blocking layer (also called a cap layer) made of p-type AlGaN on an active layer nearer to a p-type cladding layer (for example, Japanese Patent Laid-Open Publication No. hei 9-219556). FIG. 15 shows energy bands, especially the conduction band, of a conventional semiconductor laser using the p-type AlGaN electron-blocking layer. In FIG. 15, Ec indicates the bottom energy in the conduction band. In this semiconductor laser, the p-type AlGaN electron-blocking layer is considered to restrict overflow of electrons and prevent separation of In from the active layer even during operation under a high temperature and a high current.
In the conventional semiconductor laser, however, while the p-type AlGaN cladding layer usually has a thickness around 0.5 to 0.6 μm and an Al composition ratio around 0.06, the specific resistance of the p-type AlGaN cladding layer is as high as 3 to 4 Ωcm. Therefore, a large voltage drop occurs during operation due to the resistance of the p-type AlGaN cladding layer, and it is difficult to control the operation voltage not to exceed 5 V. If the p-type cladding layer is reduced in thickness, the operation voltage will certainly decrease. However, this is not an effective countermeasure because of insufficient confinement of light, failure to obtain favorable FFP (far field pattern), and other problems. Additionally, since the p-type layer contains a large quantity of Mg as the p-type impurity and therefore exhibits high absorption coefficient to light, the p-type layer existing near the active layer increases the internal absorption loss and degrades the laser property.
It is therefore an object of the invention to provide a semiconductor light emitting device reduced in operation voltage and having a favorable property by appropriate design of the distance between the active layer and the p-type layer while maintaining a thickness of the p-side cladding layer necessary and sufficient for obtaining a favorable optical property, and to provide a method capable of easily manufacturing such a semiconductor light emitting device.